3. cephadm

https://docs.ceph.com/en/latest/cephadm

cephadm is a utility that is used to manage a ceph cluster. It doesn’t rely on the credentials to access the ceph cluster, or a running mon daemon, but must be run as root. In case of ceph command cannot access the cluster, it can save us.

3.1. Deamons management

Use sudo cephadm ls to list ceph deamons run on this host (the output is in JSON format), for example:

$ sudo cephadm ls | jq -r '.[].name'
mon.las3
mgr.las3.svwbki
grafana.las3
alertmanager.las3
crash.las3
ceph-exporter.las3
prometheus.las3

The above command list names of the daemons.

cephadm can enable a ceph service like systemctl does:

$ sudo cephadm unit enable -n mon.las3 --fsid 628d3140-37c9-11f1-8f6f-d3e73c698443
Inferring config /var/lib/ceph/628d3140-37c9-11f1-8f6f-d3e73c698443/mon.las3/config
stderr Created symlink /etc/systemd/system/ceph-628d3140-37c9-11f1-8f6f-d3e73c698443.target.wants/ceph-628d3140-37c9-11f1-8f6f-d3e73c698443@mon.las3.service → /etc/systemd/system/ceph-628d3140-37c9-11f1-8f6f-d3e73c698443@.service.

Restart the service:

$ sudo cephadm unit restart -n mon.las3 --fsid 628d3140-37c9-11f1-8f6f-d3e73c698443
Inferring config /var/lib/ceph/628d3140-37c9-11f1-8f6f-d3e73c698443/mon.las3/config

Important

Do not manage ceph services by systemctl if your cluster is managed by cephadm, the ceph orchestrator is guarding these settings.

3.2. Enable a shell

$ sudo cephadm shell
Inferring fsid 628d3140-37c9-11f1-8f6f-d3e73c698443
Inferring config /var/lib/ceph/628d3140-37c9-11f1-8f6f-d3e73c698443/mon.las3/config
Using ceph image with id 'aade1b12b8e6' and tag 'v19' created on 2025-07-18 03:53:27 +0800 CST
quay.io/ceph/ceph@sha256:af0c5903e901e329adabe219dfc8d0c3efc1f05102a753902f33ee16c26b6cee
root@las3:/#

You can also specify the fsid:

$ sudo cephadm shell --fsid 628d3140-37c9-11f1-8f6f-d3e73c698443

By default, the shell is opened on mon daemon container, you can specify it using --name or -n:

$ sudo cephadm shell -n mgr.las3.svwbki
Inferring fsid 628d3140-37c9-11f1-8f6f-d3e73c698443
Inferring config /var/lib/ceph/628d3140-37c9-11f1-8f6f-d3e73c698443/mgr.las3.svwbki/config
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3.3. Destroy a cluster

The following command can destroy the cluster installed by cephadm on a node:

$ sudo cephadm rm-cluster --force --zap-osds --fsid $(ceph fsid)
Deleting cluster with fsid: 628d3140-37c9-11f1-8f6f-d3e73c698443
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